The field of the invention is high fidelity electrostatic speaker systems and more particularly, high voltage power supplies for providing the polarizing voltage for the diaphragm of an electrostatic driver in such a system.
The advantages of electrostatic type audio drivers is well known and there are numerous commercially available headphone and loudspeaker systems which employ them in lieu of the more conventional dynamic audio driver. To operate an electrostatic driver, however, a relatively high polarizing voltage must be applied to its movable diaphragm with the result that a separate high voltage power supply must be provided with the speaker system. In an electrostatic loudspeaker system, the high voltage power supply is typically mounted within the speaker enclosure and is powered by house current which is obtained by plugging the system into an electrical outlet. As a result, the loudspeaker must be positioned near an electrical outlet or unsightly extension cords must be used.
In U.S. Pat. No. 3,632,903, issued to Martin Lange, Jr., on Jan. 4, 1972, and entitled "Electrostatic Headphone," a circuit for generating a polarizing voltage from the applied audio signal is disclosed. A voltage multiplier circuit is connected to the secondary winding of a transformer which receives the applied audio signal and a capacitor is charged to the desired polarizing voltage level by a voltage multiplier circuit. Such "self-energizing" high voltage power supplies have proven quite satisfactory when used with relatively small electrostatic drivers that do not consume significant amounts of power. As a result, such self-energizing high voltage power supplies have been commercially applied to electrostatic headphones and to relatively small electrostatic loudspeakers designed to reproduce higher audio frequencies.
When large electrostatic drivers are used in a loudspeaker system to reproduce the lower audio frequencies, significantly larger amounts of power must be generated by the high voltage power supply. Because this additional power must be obtained from the applied audio signal in a self-energizing loudspeaker system, the task of diverting a portion of the power in the applied audio signal without distorting it is significantly more difficult. Also, the conversion of the applied audio signal to a high dc polarizing voltage must be performed efficiently.